A Millimeter-Wave, Transformer-Based, SiGe Distributed Attenuator

This letter presents a millimeter-wave silicon-germanium (SiGe) distributed attenuator which uses a transformer-based attenuation core. The nonlinearities of the SiGe heterojunction bipolar transistor (HBT) are managed using an RC-load, which linearizes the device impedance versus bias. In addition, a dual-resonance transformer is used to support broadband operation, while providing control over the attenuator insertion phase. Two attenuators, one using transmission line-based impedance transformers, and one using transformer-based impedance transformers, were designed and fabricated in a 180-nm SiGe bipolar and CMOS (BiCMOS) technology platform. The attenuators achieve competitive performance in terms of bandwidth and phase error, but with low insertion loss and large attenuation range.